1. Field of the invention
The present invention is related to a refrigeration unit using ammonia (an ammonia chiller unit) for small-scale refrigeration in a refrigerator, goods handling room, processing room, etc., the unit comprising a compressor, evaporation type condenser, expansion valve, brine cooler(evaporator) to perform a refrigerating cycle using ammonia as a refrigerant.
2. Description of the Related Art
In recent years measures for preventing ozone layer destruction and global warming are strongly demanded. In the field of air conditioning and refrigeration, it is urgently demanded not only not to use CFC refrigerant from the viewpoint of preventing ozone layer destruction but also to reclaim alternative refrigerant HFC and achieve improvement in energy efficiency from the viewpoint of preventing global warming.
To respond to the demands, natural refrigerants such as ammonia, hydrocarbons, air, carbon dioxide, etc. are being considered for use as refrigerants. Ammonia refrigerant is being adopted in many large-scale chilling/refrigerating plants. Furthermore, use of ammonia, a natural refrigerant, is tending to increase also in the field of small-scale chilling/refrigerating plants.
Ammonia refrigerant used for said chilling/refrigerating plants has advantages that the ozone layer destruction effect index is zero, greenhouse effect index is 1, the plant is low priced, COP is high, heat transfer coefficient is high, critical temperature and pressure are high, detection of leakage is easy, choking of expansion valve does not occur, refrigeration effect is high, etc. and drawbacks that the refrigerant is toxic, is soluble to water to be reduced to corrosive substance, is not soluble to oil, temperature at the compressor outlet is high, copper group material can not be used, etc.
Therefore, to use safely ammonia as a refrigerant, following things are required in addition that operators are conversant with safe handling method of ammonia to secure safety.
These are, first to reduce the amount of charged ammonia to a minimum, then to establish the system to be leakproof, to compose equipments constituting the system taking into consideration safety in case leakage of ammonia occurs, to improve reliability and accuracy of detecting and controlling leakage of ammonia, to prepare a measure to render leaked ammonia gas harmless. Success or unsuccess of development in the field of ammonia refrigerating machine is dependent on whether above mentioned problems are overcome and solved or not.
As a measure to reduce the amount of charged ammonia, a direct expansion type evaporation system using oil having compatibility (mutual solubility) was developed, by which the required amount of refrigerant was reduced to about 1/50 compared with that of prior types evaporation systems such as a liquid pump type and flooded system requiring a large amount of refrigerant. However, still further reduction is demanded.
As a measure to reduce the leakage of refrigerant, it is necessary to adopt a hermetically sealed or semi-sealed shaft seal of the compressor to reduce leakage from the passage of refrigerant flow. For this purpose, a compressor integrated with a canned motor, which is composed such that a highly corrosion-resistant can is provided between the rotor and stator of an electric motor to isolate the stator from an atmosphere of ammonia, has been adopted. With the compressor, ammonia gas leakage can be reduced.
As to refrigerant leakage, to positively prevent ammonia leakage from parts other than the compressor, an integral-type refrigerating machine unit has been adopted, which is a factory-fabricated packaged refrigerating machine.
Among the things to be required to secure the safety of ammonia refrigerating system mentioned before, things required further improvement are a measure to render leaked ammonia gas harmless and a further increase in operation efficiency of the refrigerating machine unit.